The present disclosure relates generally to toners and toner processes, and more specifically, to toner compositions containing an encapsulated wax.
In electrophotography, an image is produced by forming an electrostatic latent image on a surface of a photoreceptor having a drum or belt shape, or the like, developing the electrostatic latent image with a toner so as to obtain a toner image, electrostatically transferring the toner image onto a recording media such as paper directly or via an intermediate transfer member, and fusing the toner onto a surface of the recording paper by heating, or the like.
A narrow distribution of particle size of toner is desirable for use in image forming devices. When the distribution of particle size is wide, the ratio of toner having a small particle size relative to toner having a large particle size, or vice versa, may be increased. This may cause certain problems in the case of a two-component developing agent including a toner and a carrier. For example, where toner possesses a greater amount of small particles, the toner can easily adhere to the carrier and thus the ability of the carrier to retain a charge is deteriorated. In contrast, in the case of toner wherein there is a greater amount of large particles, there are problems such as a tendency for image quality deterioration because of inefficiency in the transfer of toner onto a recording media.
Toner of narrow particle size distribution can be produced by emulsion aggregation methods. Methods of preparing an emulsion aggregation (EA) type toner are known and toners may be formed by aggregating a colorant with a latex polymer formed by emulsion polymerization. For example, U.S. Pat. No. 5,853,943, the disclosure of which is hereby incorporated by reference in its entirety, is directed to a semi-continuous emulsion polymerization process for preparing a latex by first forming a seed polymer. In particular, the '943 patent describes a process including: (i) conducting a pre-reaction monomer emulsification which includes emulsification of the polymerization reagents of monomers, chain transfer agent, a disulfonate surfactant or surfactants, and optionally, but in embodiments, an initiator, wherein the emulsification is accomplished at a low temperature of, for example, from about 5° C. to about 40° C.; (ii) preparing a seed particle latex by aqueous emulsion polymerization of a mixture including (a) part of the monomer emulsion, from about 0.5 to about 50 percent by weight, or from about 3 to about 25 percent by weight, of the monomer emulsion prepared in (i), and (b) a free radical Initiator, from about 0.5 to about 100 percent by weight, or from about 3 to about 100 percent by weight, of the total initiator used to prepare the latex polymer at a temperature of from about 35° C. to about 125° C., wherein the reaction of the free radical initiator and monomer produces the seed latex comprised of latex resin wherein the particles are stabilized by surfactants; (iii) heating and feed adding to the formed seed particles the remaining monomer emulsion, from about 50 to about 99.5 percent by weight, or from about 75 to about 97 percent by weight, of the monomer emulsion prepared In (ii), and optionally a free radical initiator, from about 0 to about 99.5 percent by weight, or from about 0 to about 97 percent by weight, of the total Initiator used to prepare the latex polymer at a temperature from about 35° C. to about 125° C.; and (iv) retaining the above contents in the reactor at a temperature of from about 35° C. to about 125° C. for an effective time period to form the latex polymer, for example from about 0.5 to about 8 hours, or from about 1.5 to about 6 hours, followed by cooling. Other examples of emulsion/aggregation/coalescing processes for the preparation of toners are illustrated in U.S. Pat. Nos. 5,290,654, 5,278,020, 5,308,734, 5,370,963, 5,344,738, 5,403,693, 5,418,108, 5,364,729, and 5,346,797, the disclosures of each of which are hereby incorporated by reference in their entirety. Other processes are disclosed in U.S. Pat. Nos. 5,348,832, 5,405,728, 5,366,841, 5,496,676, 5,527,658, 5,585,215, 5,650,255, 5,650,256 and 5,501,935, the disclosures of each of which are hereby incorporated by reference in their entirety.
Some toners include a wax to assist in toner release from the fuser roll during the fusing process. In some current emulsion aggregation processes, a core latex, pigment dispersion and wax dispersion are mixed at the beginning of the toner formation process. When wax is mixed with a core latex and pigment dispersion at the beginning of aggregation and coalescence, the wax particles may become physically trapped in the mixture and act as spacers preventing the aggregation of resin particles and pigment particles. This may increase the process time for aggregation and coalescence which, in turn, may result in a longer process time. This increase in process time may contribute to the high cost of EA produced toner.
Most waxes utilized in the formation of EA toner are linear polymeric waxes, such as linear polyethylenes with a number average molecular weight of about 800 and a molecular weight distribution of about 1.1. These linear waxes may not be compatible with polymer resins utilized in toners forming a separate wax domain when incorporated into toners. These separate wax domains may become trapped in toner particles at various locations throughout the toner particles. For example, the wax particles may be trapped inside the core of a toner particle and lose their ability to function during the fusing process. Other wax particles may migrate and present themselves on the surface of toner particles, which may cause low toner flowing and transferring problems. In addition, large wax particles may form during storage, which eventually increases the size of toner particles. Attempts to remove such wax particles, such as by filtration, may result in undesirable variations in the wax content of the toner. Moreover, wax dispersions utilized in forming such toners may be unstable, which can result in large wax particle size, and high wax concentrations may be needed to obtain desired fusing performance.
Work is continuing on methods for improving the incorporation of wax into toner particles. For example, U.S. Pat. No. 5,965,316, the disclosure of which is hereby incorporated by reference in its entirety, uses a wax dispersion in water as a seed to form encapsulated wax particles, which are utilized in an emulsion/aggregation/coalescence process to form toner.
After the aggregation/coalescence process, high molecular weight wax may still be trapped inside the core of the toner particles and lower molecular weight wax may be on the surface of the toner particles. This can lead to various problems. For example, wax that is buried deep in the core of a toner particle does not contribute as much to the release function during the fusing process. Wax exposed at the toner particle surface can interfere with additive blending and reduce the time the toner may be stored before use. Thus, the ideal position of wax in toner particles is in the shell of the toner, near the surface of the particle.
Improved methods for producing toner, which reduce the time for the EA process and thus the cost, and are capable of utilizing existing processing equipment and machinery, remain desirable.